Recently, the concept of treating proliferative diseases by using drugs designed specifically against abnormally active protein kinases has been definitely proven in the treatment of CML (Chronic Myeloic Leukemia) where a first product has now been approved for successful treatment: Clinical studies showed that the drug (N-{5-[4-(4-methyl-piperazino-methyl)-benzoylamido]-2-methylphenyl}-4-(3-pyridyl)-2-pyrimidine-amine, especially in the form of the methane sulfonate (monomesylate) salt called STI571, which is sold e.g. under the tradename Gleevec®, has impressive activity against chronic phase CML. Typical for CML is a characteristic t(9;22) translocation that juxtaposes the 5′ end of the bcr gene with the 3′ end of the abl gene, resulting in a unique 210 kDa fusion protein p210bcr/abl with constitutive activity. The result is a p210bcr/abl-induced transformation ultimately leading to CML. STI571 is a reversible inhibitor that occupies the ATP binding pocket of p210bcr/abl and stabilizes the kinase in an inactive conformation. This inhibitory action appears to be the basis for its action against CML.
Overexpression or constitutive expression (activity) of protein kinases appears to be a general principle for transformations that finally lead to proliferative growth of cells and thus cancer, psoriasis or other proliferative diseases.
Overexpression or constitutive activation of the hepatocyte growth factor receptor c-Met has been observed in multiple cases of human cancer (see Fujita O S, Sugano K: Expression of c-met proto-oncogene in primary colorectal cancer and liver metastases. Jpn. J. Clin. Oncol. 1997; 27:378-383; and Liu C, Tsao M-S: In vitro and in vivo expressions of transforming growth factor-α and tyrosine kinase receptors in human non-small-cell lung carcinomas. Am. J. Pathol. 1993; 142:1155-1162). The MET receptor is overexpressed in tumors of specific histotypes, including thyroid and pancreatic carcinomas, or is acttivated through autocrine mechanisms. Moreover, the MET gene is amplified in liver metastasis of colorectal carcinomas. Receptor activation of the MET proto-oncogene triggers a unique process of differentiation called “branching morphogenesis” that involves the promotion of cell growth, protection from apoptosis and control of cell dissociation and migration into extracellular matrices. Hence c-Met had been selected as a target for cancer therapy.
The c-met gene had been sub-cloned to result in a protein fragment comprising the cytoplasmic part of the entire protein (Chan A M-L, King H W S, Tempest P R, Deakin E A, Cooper C S, Brookes P. Primary structure of the met protein tyrosine kinase domain. Oncogene 1987; 12:229-233). This construct, after hooking to a GST tag, was cloned into baculovirus and expressed in Sf9 cells. The expressed protein consists of 646 amino acids, of which the C-terminal 422 amino acids contain the kinase domain and the C-terminus of the c-Met protein and the N-terminal 224 amino acids are derived from GST and the fusion of the two proteins. The protein was partially purified by affinity chromatography on GST agarose resulting in a >90% pure preparation (SDS-PAGE).
Various other protein kinases that are involved in signal transmission mediated by trophic factors can be involved in proliferative (e.g. tumor) growth, as representative examples for protein tyrosine kinases, abl kinase, especially v-abl or c-abl kinase, kinases from the family of the src kinases, especially c-src kinase, lck, fyn; epidermal growth factor (EGF) receptor kinase or other kinases of the EGF family, for example c-erbB2 kinase (HER-2), c-erbB3 kinase, c-erbB4 kinase; members of the family of the platelet-derived growth factor (PDGF) receptor tyrosine protein kinases, for example PDGF-receptor kinase, CSF-1 receptor kinase, Kit-receptor kinase, vascular endothelial growth factor (VEGF) receptor kinase (e.g. KDR and Flt-1) and fibroblast growth factor (FGF) receptor kinase; the Insulin-like growth factor I receptor (IGF-IR) kinase, and/or serine/threonine kinases, for example protein kinase C (PK-C), PK-B, EK-B or cyclin-dependent kinases, such as CDK1, may be mentioned, all of which play a part in growth regulation and transformation in mammalian cells, including human cells.
What is desirable from the point of view of possible treatments of proliferative diseases is to have a plethora of compound classes each tailored to specific protein kinases or protein kinase classes, thus allowing to come to specific treatments. Therefore, a strong need exists to find new classes of compounds allowing for such specific inhibitory effects.